Block falls on Spring! Work and Speed!

1. Feb 1, 2005

BlasterV

A block of mass 240 grams is dropped onto a relaxed vertical spring that has a spring constant 11 N/cm as shown on the figure. The block becomes attached to the spring and compresses the spring 15 cm before momentarily stopping.

First Conversions:
240g = .24kg, 11 N/cm = 1100 N/m, 15cm = .15m

While the spring is being compressed, what work is done on the block by the gravitational force on it?

.24kg * 9.8 m/s^2 = 2.352 N
2.352 N * .15m = .3528 J -> This is definitley correct

What work is done on the block by the spring force?

Work done over distance via a function so use integration:

W = 0 to .15m ( 1100N/m x dx ) =
W = 0 to .15m ( 1100N/m x^2/2 )
W = (.15m)^2 / 2 * 1100N/m ) = 12.375 J -> No idea if this is right.

What is the speed of the block just before it hits the spring? (Assume that friction is negligible.)

This is where I have problems, I have NO idea how to find the speed of the block. I don't know how high it falls from, I tried using 9.8m/s^2 as an accel and VF = 0 in vf^2 = vi^2 + 2ad, but no go, can anyone shed light on this part?

If the speed at impact is doubled, what is the maximum compression in the spring?

No idea on this either, I don't know the answer to part 3 is probably why.

Any help on this would be great!

2. Feb 1, 2005

BlasterV

I managed to get part 3 and 4, but the Part 2 with 12.375 J is still wrong, It looks perfect to me, did I miss something?

3. Feb 1, 2005

BlasterV

Got it all even though no one helps, thanks anyway lol, someone delete this please?